SCIAMACHY takes fingerprints of trace gases

28 February 2012

The spectrometer provides us with extraordinary insights into the physics and chemistry of the Earth’s atmosphere

The SCIAMACHY spectrometer has provided us with extraordinary insights into the physics and chemistry of the Earth’s atmosphere. SCIAMACHY records the solar radiation transmitted, backscattered and reflected from the atmosphere and decomposes it into its spectral components. These results are then sifted to find spectral absorption ‘fingerprints’ of trace gases in the air. This enables researchers to draw accurate conclusions on the concentrations of air pollutants between the Earth’s surface and an altitude of 90 kilometres.

The greenhouse gas carbon dioxide (CO2) is at the top of the list of SCIAMACHY’s data collection priorities, with climate researchers particularly keen to understand the behaviour of CO2 in the global carbon cycle. Currently, around half of CO2 emissions remain in the atmosphere while the other half is absorbed by the oceans and the biosphere. Large forested areas such as those in Siberia absorb significant quantities of CO2, and it seems logical that their growth cycle would have a major influence on the amount of CO2 in the atmosphere. Measurements taken by SCIAMACHY over the northern hemisphere have confirmed this effect. In the summer months of July and August, the boreal forests ‘breathe in’ CO2 to a greater degree, thereby removing it from the troposphere. This data is of incalculable value to climate researchers.

Methane (CH4) is the third most important greenhouse gas after water vapour and carbon dioxide. Its anthropogenic emissions – primarily from rice cultivation and livestock – are highly variable, and methane is also released into the atmosphere by natural processes, for example by wetlands and thawing permafrost. A quantitative understanding of methane sources and sinks takes on particular urgency against the backdrop of the trade in greenhouse gases driven by the Kyoto Protocol. For the first time, SCIAMACHY has enabled scientists to model the global distribution of CH4. The measurements reveal increased concentrations of methane over parts of North and South America, Central Africa, India (particularly the Ganges Plain) and Indochina. In India and Indochina, atmospheric models closely matched the data recorded by SCIAMACHY. In contrast, unexpectedly large deviations were seen in parts of North and South America, in central Africa and in Indonesia. These regions contain wetlands and the intense biological activity of tropical rainforest vegetation. Scientists had previously worked on the assumption that rainforests would be more likely to reduce the proportion of greenhouse gases based on the fact that they absorb carbon dioxide. But this new data enabled them to identify a previously unknown biological process whereby rainforest plants produce methane gas – and this was the cause of the elevated measurements of methane concentration.

In early 2011, scientists working on the SeaKLIM project investigated the impact of pollutant emissions from shipping. Their results showed that international shipping releases approximately the same amount of carbon dioxide into the atmosphere as air traffic – and that it also emits 10 times as much nitrogen oxides and 100 times as much sulphur dioxide. These results were based on data supplied by SCIAMACHY.

SCIAMACHY data also has practical, everyday uses; one example is the UV check service that provides the latest updates on the risk of sunburn. By enabling people to check the current UV status on their cell phone or on the Internet, this service helps them to avoid the dangers of excessive exposure to the sun. The forecast is based on a series of different measurements, including SCIAMACHY’s data on local ozone concentrations.